HVAC actuators are used in a wide variety of HVAC systems and applications. Such actuators can include, for example, air flow damper actuators, water valves, gas valves, as well as other actuators. In many cases, a motor is used to drive the actuator between actuated positions. Typically, a controller is used to provide control signals to cause the motor to drive the actuator to a desired actuated position.
In some applications, such as some commercial applications, a number of operating characteristics are specified for the HVAC actuator. The selection of a particular HVAC actuator for a particular application is often based, at least in part, on the specified operating characteristics. The operating characteristics are typically specified over certain operating conditions. The operating conditions may include, for example, an operating temperature range, an operating voltage range, an operating current range, the age or level of use of the HVAC actuator, and/or any number of other specified operating conditions and/or parameters.
In some cases, one of the operating characteristics is a torque rating. A torque rating typically specifies the minimum torque that the HVAC actuator will produce when the HVAC actuator is operating within the specified operating conditions. For example, an HVAC actuator may have a torque rating of 5 Nm over a specified operating temperature range of −40 degrees Fahrenheit to 150 degrees Fahrenheit.
The actual torque that is produced by the HVAC actuator may vary with some or all of the specified operating conditions and/or parameters, such as temperature and/or age or level of use of the HVAC actuator. As such, in order to meet the torque rating for the HVAC actuator across all specified operating conditions and/or parameters, HVAC actuators are often produced to meet the torque rating requirement under the worst case operating conditions. Under nominal or best case operating conditions, the HVAC actuators often produce more torque than the torque rating. For example, an HVAC actuator may be desired to produce the rated torque level of the HVAC actuator when operating at the coldest operating temperature. At other temperatures, such as at nominal or higher temperatures, the HVAC actuator may actually produce more torque than is required to meet the rated torque level of the HVAC actuator, and in some cases, significantly more torque.
The variation in torque of an HVAC actuator may result from a number of factors, including the susceptibility of different components of the HVAC actuator to the various operating conditions. For example, the performance of the motor, gear train, and/or electronic controls, as well as other components, may vary with the operating conditions. It has been observed that a decrease in the operating temperature can stiffen or otherwise reduce the effectiveness of lubrication that is often used in the motor, gear train and/or actuated part, which may decrease the available motor torque that is available at the actuated part of the HVAC actuator. Likewise, significant use of the HVAC actuator over time can cause the gear train to become worn, which can also reduce the available motor torque that is available at the actuated part of the HVAC actuator over time. Thus, to meet the rated torque level under the worst case operating conditions, many HVAC actuators actually produce more torque than is required to meet the torque rating under nominal or best case operating conditions.